Diabetic Retinopathy Flashcards
1
Q
Why is diabetic retinopathy an emerging disease of epidemiological concern?
A
- 1 in 3 people with diabetes have diabetic retinopathy
- The disease is slowly progressive so it may progress to advanced stages without any symptoms and therefore without treatment
- The disease causes blindness and is a massive burden on the health system
2
Q
Describe the path of light as it enters the eye:
A
- Light entering the eye passes through the cornea (the tougher, major refractive surface)
- Light then moves through the lens
- Light then reaches the inner retina
- Light then reaches the photoreceptors of the outer retina
- Light impulses are converted by photoreceptors into electrical signals which are then transmitted to bipolar cells
- Bipolar cells transmit the signal to ganglion cells that transmit the signal to the brain via the optic nerve
3
Q
What cell types are in the neural retina?
A
Information flows in a 3 neuron chain:
- Photoreceptor cells
- Bipolar cells
- Ganglion cells
The other cell types are responsible for lateral interactions:
- Horizontal cells
- Amacrine cells
4
Q
What features of the retina are visable via opthalmoscope?
A
- Optic nerve head:
- Light disc shaped area
- Blood vessels radiate from this structure - Macula:
- Located to the left of the optic nerve head
- Darker in area
- Has fewer layers of ganglion cells so light can reach photoreceptor cells more easily - Fovea:
- Located in centre of macula in a small pit
- Has the highest concentration of cone photoreceptors
- Responsible for central vision and high visual acuity
5
Q
What are the two main blood vessel networks in the retina?
A
- Central retinal artery:
- Runs along optic nerve and supplies blood into retinal capillary networks - Choroid vascular bed:
- Recieves most of the blood flow from the central retinal artery
- Maintains the outer retina
6
Q
How is the Blood-Retinal Barrier Maintained?
A
- Endothelial cells of the retinal capillaries are joined by tight junctions which forms the inner blood-retinal barrier
- Retinal pigment epithelial cells (RPE cells) are also joined by tight junctions and maintain the outer blood-retinal barrier between the choroid the the outer retina
- If either blood-retinal barrier breaks down edema and hemorrhage can occur
7
Q
What are the 3 glial cell types in the retina?
A
- Macroglial Müller cells:
- Principle glial cell with numerous functions
- Modulates neuronal function
- Regulates the integrity of the blood-retinal barrier
- In diabetes, an excess of VEGF is produced by these cells which acts on retinal blood vessels causing a break down of the retinal-blood barrier resulting in diabetic macular oedema - Microglia:
- Resident immune cells
- In diabetes they release inflammatory cytokines (e.g. TNFa) that injure vasculature, neurons and glial cells - Astroglia
8
Q
What are the diabetic eye diseases?
A
- Diabetic retinopathy (DR): - Most common cause of vision loss in diabetics
- Disease of the retinal microvasculature with contributions from neurons and glial cells
- Involves changes to retinal blood vessels causing them to leak fluid and bleed - Diabetic Macular Oedema (DME):
- A consequence of DR that casues swelling of the macula - Cataracts:
- Clouding of the lens of the eye - Glaucoma:
- Caused by damage to the optic nerve and is associated with elevated pressure within the eye
- Diabetes nearly doubles risk
9
Q
What are the risk factors for developing diabetic retinopathy?
A
- The biggest risk factor is the duration of disease
- Other risk factors include high blood pressure, poor glycaemic control and high blood lipids
- Smoking, pregnancy and kidney disease also contribute
10
Q
What are the 3 stages of DR?
A
- Stage 1: Non-proliferative DR
- Advanced non-proliferative DR
- Proliferative DR (with neo-vascularisation)
11
Q
What are the characteristics of non-proliferative DR?
A
- Microaneurysms (focal dilations of capillaries)
- Hard intra-renal exudates (yellow deposits of lipid and protein)
- Haemorrhages (due to weakened capillaries)
12
Q
What are the characteristics of advanced NPDR?
A
- Includes the same characteristics as NPDR (microaneurysms, hard exudate and haemorrhages) as well as:
- Soft exudates (cotton-wool spots, the result of swelling of nerve axons)
- Venous bending and loops
- Intra-retinal microvascular abnormalities (abnromal retinal capillaries, may represent early stages of neovascularisation)
- Retinal schaemia (difficult to observe- main cause for increase in VEGF release)
- Acellular capillaries (not detected by opthalmoscope, due to the apoptosis of pericytes and endothelial cells in capillaries- surrounding area becomes ischemic)
13
Q
What are the characteristics of proliferative diabetic retinopathy?
A
- Neovacularisation:
- Growth of new blood vessels into vitreous cavity
- Can cause haemorrhage into vitreous cavity and retina - Fibrosis:
- From glial cells
- Can deform the retina and cause it to detach - Haemorrhage:
- Neovascularisation results in fragile vessels prone to haemorrhage - Diabetic macular oedema:
- Most important manifestation of DR
- Buildup of fluid in macula
- Leading cause of blindness in diabetic patients
14
Q
What are the current treatments for DR?
A
- Very limited
1. Glucose control
2. Blood pressure control (ACE inhibitors) - Most treatments focused on PDR and DME, not early prevention:
1. Laser photocoagulation: causes abnormal blood vessels to shrink to treat PDR
2. Vitrectomy: surgery to remove vitreous gel of eye, used to treat severe bleeding into vitreous due to PDR
3. Intra-vitreal Injection of Anti-VEGF: used to treat PDR and DME
15
Q
What are some future treatments for DR?
A
- Other anti-angiogenic agents
- Anti-oxidants
- Anti-inflammatory drugs
- Inhibition of AGE formation
- Lipid lowering drugs
